Yeah, Yahoo gives more weight to onpage aspects, especially content and keywords. That's what makes it different from Google, which allots utmost importance to backlinks.
Since meta tags have faded as a regular search optimization technique, many of us have gotten lazy about doing them at all. But adding metas can help for ad targeting, and still give you some benefits in the search index.Esp in Yahoo.
Yahoo's algorithm still puzzles me. Like most people said, Yahoo really gives importance to onpage factors, but its bots still read backlinks. I'm not quite sure how importance it is.